Carbon fiber reinforced plastic (“CFRP”) materials are increasingly being used in place of aluminum to form the skin panels and structural members of commercial airplanes. CFRP materials are advantageous compared to aluminum due to the higher strength-to-weight ratios provided by carbon composites. However, CFRP materials appear to be more susceptible to catastrophic damage from lightning strikes than aluminum materials.
Typical lightning strike related failures in CFRP materials appear to be driven by high temperatures. The carbon fibers in the composite materials become very hot when subjected to a lightning strike. The temperature may exceed the pyrolization temperature of the resin, turning the resin from a solid to a gas. The corresponding increase in internal gas pressure contributes to the damage to the structure by delaminating the layers and, possibly, puncturing the underlying systems or structure. The high temperatures can also cause permanent damage to the fibers, resulting in expansion of the fiber diameter. Localized heating in combination with material coefficient of thermal expansion also influences damage. Impact forces associated with lightning strike are acoustic, electromagnetic and pneumatic in origin. These forces can exceed material tensile strength limits at corresponding elevated temperatures.
Current solutions use electrical paths to effectively conduct and distribute the electrical current away from the lightning attachment zone in an effort to avoid sparking. These electrical paths are integrated into the CFRP material design, such as beneath an outer paint layer (e.g., a polyurethane layer). However, despite the use of well-designed electrical paths to conduct the electrical current, substantial structural damage is still being observed.
Accordingly, those skilled in the art continue to seek new techniques for avoiding structural damage resulting from lightning strikes.